Improved acoustic image reproduction system using a piezoelectric printer and electrogasdynamics

ABSTRACT

An apparatus and method for printing an image of a pattern of sound waves on a dielectric sheet, such as paper or the like, comprising the use of a space charge cloud of ionized ink from an electrogasdynamic generator to develop an electrostatic charge image of the sound pattern which has been formed on the dielectric sheet using an acoustic image converter plate. By virtue of the high charge on the ink, a high quality image is developed on the sheet even though the sound wave patterns resulting from ultrasonic scanning of a test object or from the energizing of an acoustical transducer may be comparatively weak.

United States Patent Meredith C. Gourdine West Orange, NJ. 803,02 1

Feb. 27, 1969 Apr. 6, 1971 Gourdine Systems, Inc. Essex County, NJ.

Inventor Appl. No. Filed Patented Assignee IMPROVED ACOUSTIC IMAGEREPRODUCTION SYSTEM USING A PIEZOELECTRIC PRINTER (ES), 74 (ESX), 74(P), (lnquired); 355/(lnquired); l79/100.41 (PE), (inquired), 100.1 (B);3l0/8.1; 73/(lnquired) [56] References Cited UNITED STATES PATENTS2,753,796 7/1956 Wood et al. 346/74X 3,121,873 2/1964 McNaney 346/74Primary Examiner--Bernard Konick Assistant Examiner-Gary M. HoffmanAttorneysRobert S. Dunham, P. E. Henninger, Lester W. Clark, Gerald W.Griffin, Thomas F. Morgan, Howard J. Churchill, R. Bradlee Boal,Christopher C. Dunham and Thomas P. Dowd ABSTRACT: An apparatus andmethod for printing an image of a pattern of sound waves on a dielectricsheet, such as paper or the like, comprising the use of a space chargecloud of ionized ink from an electrogasdynamic generator to develop anelectrostatic charge image of the sound pattern which has been formed onthe dielectric sheet using an acoustic image converter plate. By virtueof the high charge on the ink, a high quality image is developed on thesheet even though the sound wave patterns resulting from ultrasonicscanning of a test object or from the energizing of an acousticaltransducer may be comparatively weak.

smwesmmws I Patented April 6, 1971 INVENTOR.

IMPROVED ACOUSTIC IMAGE REPRODUCTION SYSTEM USING A PIEZOELECTRICPRINTER AND ELECTROGASDYNAMICS BACKGROUND OF THE INVENTION The presentinvention relates to the image reproduction art and more particularly toan image producing apparatus and method using an electrogasdynamicgenerator in cooperation with an acoustic or other pressure imageconverter.

Sound waves, and particularly those in the ultrasonic region havingfrequencies above 20,000 cycles per second, have been used for manypurposes in industry such as for cleaning, heating, machining, gaugingthickness and a number of other diversified applications. In recentyears sound waves have been found particularly useful in nondestructivetesting as a replacement for x-rays, since sound waves can be used topenetrate and scan the interior structure of opaque materials just asx-rays, but also they have the particular advantage of being attenuatedfar less by most materials than are x-rays or other electromagneticwaves. In addition, sound is far more sensitive to structuraldiscontinuities such as cracks, microseparations or the like and may becompletely reflected by an air gap larger then centimeters.

With the growing use of sonic test equipment has come the problem ofachieving adequate acoustic image reproduction and the need for suitableimage converter systems. Accordingly, acoustic image converter plateshave been developed which are constructed of piezoelectric crystal orsemiconductor material. A sound wave pattern striking a surface of sucha plate causes'mechanical distortion at each point on the surface, whichdistortion results in the generation of a charge across the thickness ofthe plate. An electric charge picture of the sound wave pattern is thusproduced on the opposite surface of the plate. This charge image maythen be scanned such as with a conventional television iconoscope orotherwise detected and a visual image may be reproduced by conventionaltechniques.

A major problem in connection with such acoustic image converters is theproduction of sufficient power to obtain a reasonably clear image, sincea sound power density in the range of 10 to 10" watts/cm. is requiredpresently to obtain a clear picture. It is therefore quite desirable toprovide a system which will produce a high quality visual image from aconverter image which has been produced by a sound pattern of minimumpower density.

The present invention provides such a system with the added advantage ofaccomplishing the high quality image reproduction with a minimum ofmechanical operations and at high speed.

SUMMARY OF THE INVENTION The apparatus and method of the presentinvention comprises the use of an electrogasdynamic, or EGD, generatorin combination with an acoustic or other pressure image converter forreproducing a sound pattern or the like as a printed image. Moreparticularly, the BOD generator is used as a spray gun to produce aspace charge cloud of ionized ink particles that are deposited on thesurface of a dielectric sheet to develop a latent electrostatic chargeimage thereon, which image has been derived from a chargepatternproduced by a sound wave on a piezoelectric plate converter or similarsemiconductor arrangements.

It has been observed that it is a peculiar quality of charges in anelectrogasdynamically produced cloud to tend to become uniformlydistributed over a dielectric surface and the amount of surface chargethat can be acquired by the surface has a particular limit under givenconditions. The ion concentration in the cloud determines the maximumpotential of the dielectric surface and the maximum surface charge. Anexplanation of this phenomenon is more fully set forth in my copendingapplication Ser. No. 763,854, filed Sept. 30, 1968, and assigned to thesame assignee as the present application. As a result of thisphenomenon, if a patent electrostatic image is produced on a sheet ofpaper by selectively discharging a uniform layer of charge on the sheetusing the charge pattern produced by a sound wave on a semiconductorelement, such as a piezoelectric or piezoresistive plate, the latentimage may be developed to a high quality by the highly charged particleswhich are selectively distributed eliminating fringing effects andachieving greater resolution in the halftone areas. This improvedprocess in addition provides a high speed permanent image reproduction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a system embodying theapparatus of the present invention;

FIG. 2 shows a test system which produces an input for the system of thepresent invention;

FIG. 3 shows the structural detail of an acoustic image converter whichmay be used with the present invention; and,

FIG. 4 shows an optional piezoelectric recording plate setup which maybe used with the present invention.

DETAILED DESCRIPTION The method and means of the present invention maybe best understood by first briefly describing the operation of thesystem shown in FIG. 1 which indicates all the steps to be used inproducing a printed image of a sound wave pattern. A dielectric sheet I,such as paper or other media, on which the image is to be reproduced ispassed over a grounded plate 40 along by three essential operatingcomponents which are positioned in sequence. The first component is acharge producing device, such as an EGD ionizer 2 or corona dischargedevice, and uniformly coats the surface of the sheet 1 with chargedmolecules. The charged surface is then brought into contact with thesurface of the acoustic image converter 3, a piezoelectric transducerwhich may be in the form of a plate of crystalline material such asquartz or one of the electrorestrictive ceramics such as bariumtitanate. The piezoelectric trans ducer surface 4 is charged in thepattern of an impinging acoustic wave, in a manner which will be morefully explained, and thus discharges the charge layer on the dielectricsurface in accordance with this charge pattern. The resulting latentcharge image on the dielectric surface is then passed to an EGDdeveloper 5 which produces a space charge cloud 6 ofelectrogasdynamically produced ink or toner particles that develop thecharge image producing a printed image 7 on the dielectric sheet 1.

FIG. 2 shows a particular test system which may be used in connectionwith the system of the present invention. This system comprises a soundtransmitter 8, a test object 9 and an acoustic image converter 10. Thesound transmitter 8 may comprise a piezoelectric plate driven by anelectric oscillator 11 at the mechanical resonant frequency of the platefor example, in the range from I to 10 megahertz, that is, 10 c.p.s. Thesound waves 12 produced by the plate irradiate the test object 9 with afocused parallel beam of ultrasound. Any inconsistencies or defects,such as the line 13, in the test object 9 intercept part of the beam andcause a sound shadow-graph on the face of the image converter 10, whichis in the form of a piezoelectric receiving plate made of natural quartzor, as previously mentioned, one of the electrostrictive ceramics suchas barium titanate. This plate may be constructed of any suitablepiezoresistive material sensitive to pressure, for example,semiconductors of the lead metaniobates, lead zirconatelead titanatesand the like.

As air has an excessive attenuation effect on ultrasound, the

receiving plate 10 along with the transmitting crystal 8 and the.

test object 9 may be immersed in a tank 14 of water or oil for betterpropagation.

The rising sound wave pattern causes a mechanical distortion at eachpoint on the receiving plate surface 16. This distortion results in thegeneration of a charge across the thickness of the plate 10. The highintensity of the unobstructed portions of the sound beam results in alarge electric charge on the outer surface 15 of the plate in the areasaffected while the low intensity portions of the beam, corresponding tothe defect 13 in the test object 9, results in a smaller charge patternon the face 15 of the plate 10. Since the surface 15 is clean quartz ora ceramic with a high lateral surface resistance, each point of theplate with its associated charge can be considered as independent of allits neighbors. Consequently the acoustic shadow-graph falling on theinner face 16 of the receiving plate 10 is transformed into an electriccharge picture on the opposite face 15.

Referring again to FIG. 1, it will be seen that this electric chargepicture may be developed by the system shown therein. The detailed stepsof the development are as follows. The dielectric sheet 1 on which theimage is to be printed is first coated with a uniform layer of chargedparticles by means of the EGD ionizer 2, or a corona discharge device ora similar device known in the art. The dielectric sheet 1 may be asingle piece of paper or may be a continuously fed web depending uponthe use to which the image is to be put. The charged sheet is supportedon the grounded member 40, which may be a metal plate, and is thenbrought into contact with the charged surface 4 of the piezoelectrictransducer 3. The surface 4 is charged in accordance with an impingingsound wave pattern in a manner such as described in connection with FIG.2. The uniform charge layer will be discharged in the appropriate areasin accordance with the charge image on the surface of the piezoelectricplate leaving a latent electrostatic image of the sound wave pattern.This charge image is then developed by means of the electrogasdynamicdeveloper 5.

In the developer 5, the ink or toner to be used for printing the imageis sprayed into an atomizing chamber 17 from an appropriate reservoir18. The droplets of ink or particles of toner in the chamber arecirculated in a counterclockwise direction by a fan 19. An EGD gun 20 ispositioned in the chamber 17 and ionizes the passing ink droplets toproduce an electrogasdynamic space charge cloud 6. An acceleratorelectrode 30, located at chamber opening 31, sets up an electro' staticfield which urges the charged particles in the cloud 6 toward thegrounded plate 40 when reaching the region of the opening. The ionizedink will tend to distribute itself evenly over the charged surface ofthe sheet. 1 clinging to the uncharged areas and being repelled by theoppositely charged particles in other areas until a uniform potentialand evenly distributed charge layer is reached. Theelectrogasdynamically produced ink particles which are highly chargedtend to concentrate themselves in the uncharged areas and will notadhere to the highly charged areas so that an ink image is producedwhich directly corresponds to the distribution of the charge imageproduced by the piezoelectric plate 4.

As a result of the even distribution of charged ink, fringing effectsare avoided at the areas of greatest contrast and as the highly chargedparticles will avoid those areas already charged to maximum potential,an image with improved definition and resolution is developed. A varietyof inks, toners or paints may be used in this process due to theversatility of the EGD spray gun in charging aerosols and the use ofwater based inks is particularly of advantage in avoiding air pollutionproblems during the subsequent fixing step if one is desired.

FIG. 3 shows an alternate form of image converter utilizingsemiconductors and thin films. This converter comprises a thinconductive metal film 21, a layer of piezoelectric and possiblyrectifying semiconductor material 22 exhibiting highly lateralresistivity, dots of independent, electroluminescent material 23 andanother thin transparent metallic coating 24. A sound wave picturestriking the conductive film 21 is converted to a pattern of electriccurrents moving through each tiny area of the semiconductor 22. Thesecurrents may be intrinsically amplified by various arrangements.Arriving at the luminescent dots 23, the currents cause each dot to glowwith an intensity proportional to the strength of the'exciting current.Ultimately this current strength is deter mined by the sound strength ofeach small area of the arriving sound wave pattern. Thus, the soundpattern is converted to a visual picture without the use of complexcathode ray tubes or other devices. The resulting visual picture may beprinted in the manner of the present invention by using it incombination with a xerographic plate 25 to produce a correspondingcharged surface image. The xerographic plate 25 may then be substitutedfor the piezoelectric plate 4 in the system of FIG. 1. Other methods andapparatus for developing the charge image on the surface of thexerographic plate 25 are more fully disclosed in my copendingapplication, Ser. No. 763,722, filed Sept. 30, 1968, and assigned to thesame assignee as the present application.

While the present invention has been described for use with acousticimages, it will be seen that the piezoelectric plate can reproduce manytypes of pressure images in the form of a charge pattern on the faceopposite the one on which the pressure is applied. For example, as shownin FIG. 4, a printing mat 26 having type face 27 on its surface may beimpressed against a piezoelectric plate 4a and a charge image of thetype 27 will be produced on the opposite face of the plate 40. Thischarge image may accordingly be used to produce the latent electrostaticimage in the system shown in FIG. 1.

Thus an improved image reproduction system is presented for printing anacoustical or other pressure type pattern using a piezoelectrictransducer in combination with an electrogasdynamic developer to achievehigh resolution and high speed image printing.

lclaim:

1. A printing apparatus comprising:

a. means for depositing a layer of electrostatic charge on the surfaceof a dielectric sheet;

b. piezoelectric means for producing patterns of electrically conductiveareas on a surface in response to impressed pressure patterns;

0. means for bringing the dielectric sheet in contact with saidconductive surface so that a latent electrostatic image of the pressurepattern is formed on said sheet; and

d. means for electrogasdynamically producing and directing a cloud ofionized particles against a surface of said sheet to develop said latentelectrostatic image.

2. Apparatus as claimed in claim 1 wherein said piezoelectric meanscomprises a member of piezoresistive semiconductor material.

3. Apparatus as claimed in claim 1 wherein said piezoelectric meanscomprises a quartz plate.

4. Apparatus as claimed in claim 1 comprising:

e. electroluminescent means for producing light patterns in response tothe patterns produced by said piezoelectric means; and

f. xerographic means for producing patterns of electrically conductiveareas on its surface in response to light patterns produced by saidelectroluminescent means.

5. Apparatus as claimed in claim 1 wherein said piezoelectric meanscomprises a plate having one surface in contact with a sound conductingmedium and its other surface producing electrically conductive areasthereon in response to sound patterns impinging on said one surface.

6. Apparatus as claimed in claim 5 wherein said sound conducting mediumis contained in an enclosure.

7. A method of printing, comprising the steps of:

a. depositing a uniform layer of charge on the surface of a dielectricsheet;

b. bringing the charge layer in contact with the face of a piezoelectricmember having a voltage pattern thereon resulting from the impressing ofa pressure pattern on its opposite face thereby producing a latentelectrostatic image of the pattern on the dielectric sheet; and

c. developing the latent electrostatic image by means of anelectrogasdynamically produced cloud of ionized particles.

8. The method as claimed in claim 7 wherein the pressure patterns aresound waves.

9. The method as claimed in claim 7 wherein the piezoelectric member iscomposed of a piezoresistive semiconductor material.

2. Apparatus as claimed in claim 1 wherein said piezoelectric meAnscomprises a member of piezoresistive semiconductor material. 3.Apparatus as claimed in claim 1 wherein said piezoelectric meanscomprises a quartz plate.
 4. Apparatus as claimed in claim 1 comprising:e. electroluminescent means for producing light patterns in response tothe patterns produced by said piezoelectric means; and f. xerographicmeans for producing patterns of electrically conductive areas on itssurface in response to light patterns produced by saidelectroluminescent means.
 5. Apparatus as claimed in claim 1 whereinsaid piezoelectric means comprises a plate having one surface in contactwith a sound conducting medium and its other surface producingelectrically conductive areas thereon in response to sound patternsimpinging on said one surface.
 6. Apparatus as claimed in claim 5wherein said sound conducting medium is contained in an enclosure.
 7. Amethod of printing, comprising the steps of: a. depositing a uniformlayer of charge on the surface of a dielectric sheet; b. bringing thecharge layer in contact with the face of a piezoelectric member having avoltage pattern thereon resulting from the impressing of a pressurepattern on its opposite face thereby producing a latent electrostaticimage of the pattern on the dielectric sheet; and c. developing thelatent electrostatic image by means of an electrogasdynamically producedcloud of ionized particles.
 8. The method as claimed in claim 7 whereinthe pressure patterns are sound waves.
 9. The method as claimed in claim7 wherein the piezoelectric member is composed of a piezoresistivesemiconductor material.
 10. The method as claimed in claim 7 wherein thepressure pattern receiving face of said piezoelectric member iscontained in an enclosure.